Process of photographic printing



UNITED STATES PATENT OFFICE.

REDFIELD B. NVEST, OF GUILFORD, CONNECTICUT.

PROCESS OF PHOTOGRAPHIC PRINTING.

t-BPECIFICATION forming part of Letters Patent No. 345,753, dated. July 20, 1886.

Serial No. 167,299.

(No sprr-imrns To all whom it may concern.-

Be it known that I, REDFIELD B. XVEsT, of Guilford, in the county of New Haven and State of Connecticut, have invented a new Improvement in Photographic Printing; and I do hereby declare the following to be a full, clear, and exact description of the same.

This invention relates to an improvement in photographic printing, and is an improvement on the invention for which Letters Patent of the United States No. 273,206 were granted to me February 27, 1883; and it consists in the processes as hereinafter described, and particularl y recited in the claims.

1. To sensitize the umen-To produce the best results the paper is first coated upon both sides with a starch solution, which forms the subject of an application for patent filed on even date herewith. The seusitizingsol ution is prepared from the following formula: Potassium bichromate, eight parts; mercuric chloride, four parts; aluminum sulphate, one part. For convenience these may be in powder. For the bath take pure water, according to the size of the bath, and to each ounce of water add fifty grains of the above-mentioned compound and thoroughly dissolve the same in the water. The paper is immersed in the bath, so as to wet both sides, not to exceed one minute. Care should be taken to protect the paper during and after the sensitization from chemically active light, as it is more sensitive than paper prepared under the usual process for photographic printing. The paper is dried may be by artificial heat, but coal-gas or kindred vapors should be avoided as injurious to the surface, and the paper thus sensitized should be used the same day to produce the best results, but it may be kept several days in a dark, cool, damp place. The one part of aluminum sulphate may be omitted, if less contrast is desired, without materially affecting the result. I therefore do not wish to be understood as limiting this part of my invention to the use of aluminum sulphate.

2. l rintiag.The glass negative for printing with paper thus sensitized should be thinner than that used for silver-printing, in order to prevent too deep shadows and bronzing during the development. If, however, it is necessary to use a thicker negative, roughen the varnish over its most transparent parts with retouching-powder. The printing should be carefully watched during its progress, and should be carried only so far as to make visible all that it is desired to show in the finished print. Vhen a sufficient number of prints have accumulated, they must be washed for twenty or thirty minutes in clear water and then developed.

3. D02 cZ0pin .-The compound from which the developing-bath is made is from the following formulaz' gallicacid, fifteen parts; pyrogallol, one part; ferrous sulphate, fifteen parts; sodium hyposulphite, (dried,)onehundred parts; aluminum and ammonium suiphate, (dried,) fifteen parts; potassium bitartrate, twelve parts. These should be kept in stock dried. Each of the ingredientsre quired dried is obtained so by fusing the commercial article and maintaining it in that condition until the water of crystallization is driven off. This process of drying is necessary to prevent decomposition of the con1- pound. If possible, the ingredients should be in a fine granulated condition rather than in powder. The proportions called for above are weighed out after the materials have been dried. \Vheu mixed, they should be immediately packed in tightdry bottles. The compound will then keep indefinitely.

To prepare the developingbath it should be made the same day that it is required for use. Add ten grains of the dried composition to each ounce of water.

The test of the good working quality of the ingredients may be made as follows: After the solution has stood for twenty minutes it should not indicate an inky appearance or any trace of it, but,ou the eontrary,should remain colorless for at least twenty-four hours. The print should be developed in from five to ten 1ninutes, but prolonged immersion should not reduce the intensity of the print. Ifit is so reduced,an excess of acid is indicated. If the development of a cabinet print in two fluid ounces of bath should produce an inky ap pearance of the bath or trace of it, it would indicate an excess of alkali in the bath,which should be corrected. Two fluid ounces of the bath is an ample allowance for each cabinet print to be developed. Several prints may be developed in succession, if the bath is allowed to repose some minutes between the de velopment of each print. During the (leveloping operation the bath should be rocked, butin no case should the bath be crowded.

The method of developing is as follows: After the prints have been washed for twenty or thirty minutes, they are placed in the developing-bath until their color changes from yellow or light brown to violet black. The development is completed. when on holding the print up to the light,no brown tint is seen in the shadows. \Vhen it has arrived at this condition, a prolonged immersion in the developer will produce no change either in the shadows or high lights. If, however, the print has become bronzed by prolonged exposure, it will not perfectly develop. To prevent this bronzing, which occurs from a thick negative, the clearer portions should be dcadened either by an application to the back or by roughening the varnish with rctouchingpowder.

4. Blcaching.-Aftcrthe printhas been taken from the developingbath it should be thoroughly rinsed in pure water; but the whites will not be sufficiently pure without more or less bleaching. For this purpose a bath from the following formula is prepared: bromine, one ounce; bromide of potassium, two ounces; water, ten ounces. This should be kept from the light. \Vhen it is required to bleach the whites of prints, add enough of the bleaching solution to water to color light yellow or amher. Then immerse theprints until sufficiently whitened. If the shadows are too dark, add .a little acetic acid to the bath. A. deep bath will produce better results than ashallow one. As soon as the prints are bleached, they may be at once mounted if the color is satisfactory; if not, they may be transferred to the toningbath.

5. Toning.l employ the following formula for the preparation of the compound for the toning-bath, and which may be kept in stock: potassium nitrite, four parts; lead nitrate, one part. The potassium nitrite may be prepared from potassium nitrate or saltpeter by melt-' ing in a crucible and keeping at a red heat for two hours. For the toning-bath, for each ounce of water add five grains of the toning compound. The prints are immersed in this bath after bleaching. \Vheu acetic acid has been added to the bleaehingbath, it is better to wash the prints before toning. This toning, it will be observed, is the reverse of silver toning. If a csld gray and black are desired, a trace of mercuric chloride added to the bath will produce that result. A larger proportion of the mercuric chloride will produce agreenish black.

\Vhile I have obtained the best results from the proportions of the ingredients of the several baths, as I have described, these proportions may be varied to some extent without materially changing the result. I do not therefore wish to be limited to the precise proportions which I have described.

I am aware that a bath for the treatment of paper for photographic purposes has been made from a combination of many ingredients, among which are bichloride of mercury ,and bichromate of potash; but in such combination ofother ingredients with the bichloride of mercury and the bichromate of potash the result due to the bath composed of bichloride ofmercury and bichromate of potash only, and in the proportions which I have described, cannot be attained. The essential feature of this part of my invention resides in a bath composed of potassium biehromate and mercuric chloride in certain proportions, as described.

I claim- 7 1. The'herein-described improvement in the process for photographic printing, consisting in subjecting the paper to be printed upon to a bath composed of potassium bichromate and mercuric chloride, in the proportions and substantially as described.

2. The hereindescribed improvement in photographic printing, consisting in subjecting the print to a bath composed of gallic acid, pyrogallol, ferrous sulphate, sodium, hyposulphite, aluminum and ammonium sulphate, and potassium bitartrate, in the pro portions and substantially as described.

3. The herein-described improvementin photographic printing, consisting in subject ing the print after development to abath composed of bromine, bromide of potassium, and water, in the proportions and substantially as described.

REDFIELD B. VEST.

.Vitnesses:

CHRISTOPHER SPENCER, FRED C. SrnNoER. 

